Gate for conveyors



United States Patent Ofl" 3,199,149 hatented Aug. 10, 1%65 GATE FUR CGNVEYQRS Robert J. McKnight, Springfield, and Robert W. Gotham, Summit, N.J., and (Ian-1.7. Falcon, Grand Rapids, Mich, assignors to The Rapids=Standard Company, linen, Grand Rapids, Mich, a corporation of Michigan Fiied Mar. 20, 1963, Ser. No. 266,610 filaims. (43E. 16-1) This invention relates to conveyor gates, and more particularly to a pivoted conveyor gate which combines easy operation with positive action through the use of a novel system of spring balancing.

Conveyor gates are customarily provided in long conveyors running through factories or warehouses at points where aisles cross the conveyor. As such crossing points, a section of the conveyor can be pivotally swung open so as to permit the passage of personnel or vehicles. Customarlly, these gates are hand-operated and rely on the physical strength of the operator to lift them from the closed into the open position. Such an arrangement is adequate when the conveyor is narrow and the gap is small, but when the conveyor is wide and heavy and the gap extensive, the weight of the swingable section becomes such that its manipulation by hand becomes impossible or at least impractical.

The present invention provides a method of construction which makes possible the manual operation of very heavy conveyor gates without excessive etiort by persons of ordinary strength. The invention accomplishes this result by providing a system of counterbalancing springs which act on the gate section during different increments of motion in such a manner and direction as to completely counterbalance the gate through most of its range of movement on both sides of the vertical position except near the extremities of its motion, at which extremities the weight of the conveyor is allowed to become effective to a suficient degree to maintain the gate section steadily in either of its extreme positions.

It is therefore the object of this invention to provide a conveyor gate which is biased to a limited degree into either the fully open or fully closed position by its own weight, yet which is substantially completely counterbalanced between its two extreme positions for easy movement between the two extreme positions.

it is a further object of the invention to achieve the above result by the use of a plurality of springs which act on the conveyor gate during various portions of its motion.

It is a still further object of the invention to provide FIG. 2 is a side elevation of the same gate in the open position;

FIG. 3 is an enlarged detail view of the device of FIG. 2;

FIG. 4 is a graph showing the movements acting on the gate as a function of the gate an le;

FIG. 5 is a schematic diagram showing the linear and angular relationships of the various parts of the inventive device;

FIG. 6 is a plan View of an alternative embodiment of the invention showing the gate in the closed position; and

FIG. 7 is an end elevation of the device of FIG. 6 but showing the gate in a vertical position.

Basically, the principle of the invention consists of providing in association with the swingable gate section a spring carrying member whose one end is pivotable about an axis parallel to the pivot axis of the gate section but spaced therefrom, and which is slidably supported near its other end by an element which is rigidly fixed to the gate section itself. Springs are provided on the spring bar in such a manner that each spring or group of springs has one extremity acting against a stop fixed with respect to the spring bar, and the other extremity acting against the member which is rigidly fixed with respect to the gate section itself. By providing a spring and stop on each side of the rigidly fixed member, it becomes possible to counterbalance the gate against gravitational movement in one direction on one side of the vertical, and in the other direction on the other side of the vertical.

The exact action of the springs will be more readily understood from a consideration of the drawings, in which FIGS. 1 and 2 illustrate typical extreme positions of the gate. In FIG. 1, the gap 14 between conveyor sections 12 and 14 is bridged by a gate section 16 provided with a pair of arms 18 which are arranged for free pivotal movement about a pivot shaft 20. Alignment means 22, 24 may be provided to assure proper longitudinal alignment of the gate 16 with the conveyor sections 12 and 14 when the gate 16 is closed. A bracket 26 is fixedly attached to the gate section 16. The bracket 26 has an aperture which supports the spring bar 28 but allows it to slide longitudinally with respect to the bracket 26. The spring bar 28 is hinged on a pivot shaft 36 and is provided with fixed stops 32, 34 respectively. As best seen in FIG. 3, the pivot 30 is vertically adjustable in a slot 31 so as to permit continuous variation of the spring characteristics to fit specific embodiment by modifying the force diagram of FIG. 5. An examination of FIGS. 1 and 2 will readily show that in the closed position, springs 36, 38 and 40 are compressed between stop 34 and bracket 26 while spring 42. is unstressed; and that in the open position, spring 42 is compressed between stop 32 and bracket 25 while springs 35, 38- and 4d are unstressed. Alternatively, it may be desirable to so dimension the springs that springs 3e, 38 and 4d are still slightly compressed when bracket as engages spring 42, to avoid rebound of the gate at that point.

As will be readily seen from FIG. 3, the springs 36, 38, 49 may be of unequal strength. The reason for this arrangement will best be understood from a consideration of FIG. 4, which shows in diagrammatic form the relative efiects of the weight of the gate section 16 and of the various springs throughout the range of movement of the gate section To.

In FIG. 4, curve 5% shows the moment produced by the weight of gate 16 as a function of the angle between the gate and the conveyor. It will be understood that on the left-hand side of the line in FIG. 4, this moment is clockwise in FIGS. 1 and 2, whereas on the right-hand side of the 90 line of FIG. 4, the moment is counterclockwise in FIGS. 1 and 2. Curve 52 in FIG. 4 shows a typical counterbalancing moment curve or spring moment curve for the device shown in FIGS. 1 through 3. By comparison, curve 54 of FIG. 4 shows the spring moment if only a single spring is used in the device of FIGS. 1 through 3, instead of the three springs 36, 38 and 40. It Will be readily seen by comparison of curves 5% and 52 that the quantity B shown at each end of the diagram of FIG. 4 represents the locking bias with which the gate is biased into either of its extreme positions.

- In accordance with the invention, the objective of using multiple springs in a device of this nature is to make the spring or counterbalance moment curve coincide as closely as possible with the weight moment curve. In practice, this means that, disregarding friction, the vertical distance between the two curves (i.e. the difference in moments) must never exceed a quantity which would make it difficult for an operator to move the gate manually, taking into account the distance from the gate pivot of the point at which the operator can conveniently apply his hand-s. :In other words, if W is the weight of the gate and 1 the distance between the gate pivot 29 and the center of gravity of .the gate (CG), and if k is the distance between the gate pivot and the lifting handle 44-, and if further the operator is capable of conveniently lifting only S percent of the weight of the gate at the operating handle 44 in the absence of any counterbalancing forces, then the requirement for the device can be written as 1 MGMS=S%W l/"k at any angle a If a maximum closing bias for the gate is desired, Equa tion 1 can be supplemented by the complementary equa tion (2) M M ;=S%W 1/k for a==0 In both of the above equations, it will be understood that M is the moment caused by the weight of the gate, and that M is the moment caused by the springs.

Modification FIGS. 6 and 7 show a modified embodiment of the invention which is similar in .all'respects to the embodiment of FIGS. 1 through 3, except that instead of a single spring bar 28 carrying three springs 36, 38, 40, three spring bars 60, 62, 64 are provided. Each of the spring 7 bars 60, 62 64 carries an individual spring 66, 68, 70 of different length and strength. Normally, the weakest spring would be of such a length as to be completely distended and in contact'with bracket 26 when the gate 16 is vertical. The other springs would then have their upper ends at distances a and 0 from bracket 26 when they are completely distended and the gate 16 is vertical. Each of the springs 66, 68 and 7t) abuts at its lower end against a stop 34 corresponding in function to the stop 54 of FIGS. 1 through 3. Likewise, the spring 42 of the embodiment of FIGS. 1 through 3 may be split into a plurality of springs 42' in the embodiment of FIGS. 6 and 7. Each of the springs 42' extends between the bracket 26 and a stop 32 corresponding in function to the stop 32 of the embodiment of FIGS. 1 through 3.

It should be understood that it is within the teachings of the inventionto provide any number of spring bars and any number of springs or combinations of springs on each bar to meet the requirements of a particular situation.

It will be seen that the present invention provides a structure and method by which a very heavy conveyor gate can be spring-counterbalanced in such a manner as to be operable throughout itsentire range by a single human operator without special tools, and yet is securely biased by its own weight into each of the extreme closed or open positions. Obviously, the invention can be carried out in many dilferent ways of which the emb-odi nients described herein areonly illustrative. Therefore, I do not desire to be limited by the illustrative embodi- 4 rnents shown, but only by the scope of the following claims.

' I claim:

1. Counterbalancing mechanism for a pivoted comeor gate, comprising: pivot means having an axis parallel to but offset from the axisof the gate pivot; guide means pivotally mounted on said pivot means and slidably received in an abutment member fixed with respect to said gate; first spring means extending on said guide means between said abutment member and first stop means on said guide means between said pivot means and said abutment means; and second spring means extending on said guide means between said abutment member and second stop means on said guide means on the opposite side of said abutment means from said pivot means; the spatial relationship between said pivot axes being such that said gate is substantially free of spring forces when it is vertical but that said first spring means operate to impede its movement toward the horizontal in one direction and said second spring means operate to impede it in the other direction. V

2. The device of claim 1, in which said pivot means are movable in a direction generally normal to their said are movable'in a direction generally normal to their said' axis and to said gate in its closed position.

7 4. The device of claim 1, in which said second spring means are completely distended when the angle between said gate and the closed position of said gate is acute, and said first spring means are completely distended when said angle is obtuse.

5. The device of claim 1, in which said. gate is movable between a closed position and an open position through an arc in excess of ninety degrees, and said spring means are of such force characteristics as to substantially counterbalance the gravitational forces acting on said gate throughout said are except in the immediate vicinity of said closed and open positions.

6. The device of claim 1, in which said gate is movable between a horizontal closed position and an inclined open position through a vertical position, and said first spring means are of such force characteristics as to substantially counterbalance the gravitational forces acting on said gate throughout the entire are between said vertical position and said closed position except in the immediate vicinity of said closed position.

7. Counterbalancing mechanism for a pivoted, generally horizontal conveyor gate, comprising: pivot means having an axis parallel to but otfset from the axis of the gate fpivot; said gate having varying gravity force applied thereto depending upon its pivotal angle between open and closed positions; fixed bracket means attached to said gate, spaced from said pivot means; elongatedspring retention means having first end portions pivotally mounted on said pivot means, and extending along the conveyor gate from said pivot means into sliding engagement with and through said bracket means; stop means between said pivot meansand bracket means; second stop means between said bracket ,means andthe end portions of said spring retention means opposite said first end portions; a plurality of compression springsbetween said first stop means and said bracket means and said second stop means and said bracket means; said compression springs having different compressive characteristics and "being mounted on said spring retention means in cooperative fashion to cooperatively 'successively cause additive biasing forces ofvarying amounts approximately the same as the gravity forces applied to the gate at'different angular positions from near full open to near full closed posit-ions, and a substantially lesser biasing force at full open and full close positions of said gate to provide stability in such latter positions. v

8. The device of claim 7, in which saidplurality of springs are'mounted on separate guide means, said stop 5 means on said guide means being so positioned and said springs being of such lengths that said abutment means engage increasing numbers of springs at discrete intervals during said movement of said gate toward its horizontal position.

9. The device of claim 8, in which said successively engaged springs are of increasing strength.

10. The device of claim 7, in which said plurality of springs are of difierent strengths and are mounted on said guide means in such a manner that upon movement of said gate toward its clesed position, said springs each become fully compressed substantially before full compres- :sion of the next stronger of said springs.

References Cited by the Examiner UNITED STATES PATENTS DONLEY J. STOCKING, Primary Examiner. 

1. COUNTERBALANCING MECHANISM FOR A PIVOTED CONVEYOR GATE, COMPRISING: PIVOT MEANS HAVING AN AXIS PARALLEL TO BUT OFFSET FROM THE AXIS OF THE GATE PIVOT; GUIDE MEANS PIVOTALLY MOUNTED ON SAID PIVOT MEANS AND SLIDABLY RECEIVED IN AN ABUTMENT MEMBER FIXED WITH RESPECT TO SAID GATE; FIRST SPRING MEANS EXTENDING ON SAID GUIDE MEANS BETWEEN SAID ABUTMENT MEMBER AND FIRST STOP MEANS ON SAID GUIDE MEANS BETWEEN SAID PIVOT MEANS AND SAID ABUTMENT MEANS; AND SECOND SPRING MEANS EXTENDING ON SAID GUIDE MEANS BETWEEN SAID ABUTMENT MEMBER AND SECOND STOP MEANS ON SAID GUIDE MEANS ON THE OPPOSITE SIDE OF SAID ABUTMENT MEANS FROM SAID PIVOT MEANS; THE SPATIAL RELATIONSHIP BETWEEN SAID PIVOT AXES BEING SUCH THAT SAID GATE IN SUBSTANTIALLY FREE OF SPRING FORCES WHEN IT IS VERTICAL BUT THAT SAID FIRST SPRING MEANS OPERATE TO IMPEDE ITS MOVEMENT TOWARD THE HORIZONTAL IN ONE DIRECTION AND SAID SECOND SPRING MEANS OPERATE TO IMPEDE IT IN THE OTHER DIRECTION. 